1. Field of the Invention
This invention relates to the manufacturing of polarizers, color filters, and polarizing filters, which are used in display applications. In particular, color liquid crystal displays for projection and direct viewing, rely on such polarizers, and filters for their operation. In the field of 3-D movies, and 3-D computer displays which employ polarization coding of the stereo image pair, use large sheet polarizers. The field also relates the fabrication of micropolarizer arrays for shutters, light valves, and 3-D displays.
2. Description of Prior Art
At present, most laptop computers use monochrome liquid crystal displays, LCD, and recently 14" color LCD's have been announced. It is projected that in the late 90's, LCD's will capture more than 50% share of the display market, and CRT-based displays will lose their dominance. FIG. 1 a illustrates a cross section 1 (side view) of a portion of an active matrix twisted nematic liquid crystal display and FIG. 1 b, a top view of the display showing a pixel array. Each pixel has a thin film transistor, TFT, 3 and either red 7, green 8, or blue filter. The liquid crystal 2 is sandwiched between two parts, The Upper Part and The Lower Part. The Upper Part has a transparent indium-tin-oxide (ITO) electrode 5, the filters 7,8,9, and upper glass substrate 10, a polarizer 11, and back light source 13. The Lower Part has the TFT's 3 fabricated on the a layer of silicon nitride, SiN, on the lower glass substrate 4, and a second polarizer. The TFT 3 is made of amorphous silicon 17, one side of which is the drain 14, and the other is the source 15 which applies a voltage to the liquid crystal through a second transparent ITO electrode 6. The gate 17 is deposited on the glass substrate 4 and is insulated from the amorphous silicon 17 by the SiN layer. Different LCD technologies are described by Mamoru et al, Society of Information Display, SID 88 DIGEST, p242 1988, and M. Katayama, et al, Society of Information Display, SID 88 DIGEST, p 310, 1988, and Kenichi Niki, et al, Society of Information Display, SID 88 DIGEST, p 322, 1988.
The yield, and hence the manufacturing cost of LCD, its performance, brightness and contrast, are affected by three main elements: the TFT fabrication which involves several steps, and the RGB filter which also involves numerous steps and the polarizer efficiencies. Each color filter is made on a separate substrate, patterned, and then transferred to the upper glass substrate 10. This is done in a sequential manner, with each color requiring 4 to 5 steps. Prior art approaches to making filters remain plagued with problems of reproducibility, color control, and high cost. Proposals to solve some of the problems are found in the papers by William Latham et al, Society of Information Display, SID 87 DIGEST, p 379, (1987), and by Donald Bolon et al, Society of Information Display, SID 87 DIGEST, p 395, (1987).
The other element affecting the performance of LCD is related to the efficiency of the polarizers. As described in the paper by T. Nagatsuka et al, Society of Information Display, SID 85 DIGEST, p74 (1985), proper preparation of the polarizers improves the brightness and the contract of LCD. The biggest problem with prior art sheet polarizers used in LCD's remains unsolved. Because they use stretched polyvinyl alcohol, the conversion efficiency of unpolarized light to polarized light cannot exceed 50%. In fact it is limited to about 45% for the best and costliest polarizers. This translates into at least a factor 2 wasted power, requiring brighter light source 13 and added weight to portable computers.
In my co-pending application Ser. No. 07/554,743, entitled "Micro-Polarizers for Window Shutters, Light Valve, and Display Applications", I describe a method for making window shutters which depends on micro-polarizer arrays as shown in FIG. 1 c. The shutter 17 comprises a first movable micropolarizer 18, a second fixed micropolarizer 19, and image frame 20 (transparent in the case of a simple window), and a translation means 21 which controls the motion of said first micro-polarizer. Each micro-polarizer consists of an array of micro-polarizing strips which have alternating polarization states P1 and P2. Moving one array with respect to the other, the window can be changed from transparent to opaque. In the transmission mode, the prior art polarizers have efficiencies less than 50% and therefore lose half the brightness when the shutter is in the transparent state.
All prior art apparatuses which rely on polarizers in the transmission mode lose at least half the brightness. There is no prior art that teaches how to produce large sheets of polarizers to be used in the transmission mode with efficiency approaching 100%. There is a method by which nearly 100% polarization efficiency is theoretically produced in the reflective mode, it is described by Martin Schadt, and Jurg Funfschilling, Society of Information Displays, SID 90 DIGEST, p 324 (1990). It uses new reflective polarizing filters made of cholesteric liquid crystal silicones (CLCS) polymers described by Martin Schadt and Jurg Funfschilling, Society for Information Display, SID 90 DIGEST, p 324 (1990). This prior art pertains to projection displays and does not teach how to make large area polarizing filters with 100% efficiency in the transmission mode as required by large area direct view liquid crystal displays, and the large area micro-polarizer window shutter in FIG. 1 c.